Common voles (Microtus arvalis) in groups of nine to 10 animals were inoculated per os with a dose of 1, 10, 1×10², 1×10³, and 1×10⁴ oocysts of the K1 strain of Toxoplasma gondii. All the common voles inoculated with 1 to 1×10³ oocysts remained subclinical and survived. Three of the 10 voles inoculated with 1×10⁴ oocysts died between days 7 and 12 post inoculation (p.i.). Antibodies were demonstrated in all the infected voles killed on day 60 p.i. The highest antibody titres in voles detected by the dye test (DT) and latex agglutination test (LAT) were 1,024 and 1,280, respectively.